As a basic method for picking up an object image in three dimensional, it has been known to shoot an object using two television cameras each disposed at a given angle to the object, the output signals from these two television cameras being alternately selected for every field. FIG. 5 illustrates diagrammatically the configuration of such a three-dimensional image pickup apparatus. In FIG. 5, shown on side A of the dashed line is a three-dimensional image pickup apparatus, while a three-dimensional display apparatus is shown on a side B. In this figure, the numeral 1 indicates an object, the numeral 2 a television camera A, and the numeral 3 a television camera B, each of the television cameras A and B having a lens disposed forwardly of an imaging screen provided therein. These are combined with a synchronizing signal generator 4, a switch 5, and an adder 6 to compose the three-dimensional image pickup apparatus. The three-dimensional display apparatus comprises a sync separator 7, a monitor television 8, and a pair of glasses 9.
Since the three-dimensional image pickup apparatus and three-dimensional display apparatus having the above configuration are well known in the art, only a brief description is given herein, and the three-dimensional image pickup apparatus will be described. The television cameras 2 and 3 are disposed forming a given angle .theta. between them with respect to the object 1. The scanning timings of the television cameras 2 and 3 are in synchronizing relationship with each other. For this purpose, the synchronizing signal generator 4 supplies pulse signals necessary for driving the television cameras, simultaneously to the television camera 2 and the television camera 3 (the television camera 2 corresponds to the human right eye, and the television camera 3 to the human left eye). The video signals from the television cameras 2 and 3 are respectively supplied to terminals a and b of the switch 5. The switch 5 is controlled by field pulses supplied from the synchronizing signal generator 4, alternately switching the output signals at the terminal c of switch 5 from field to field in such a way that the video signal fed from the television camera 1 is output in the first field and that the video signal fed from the television camera 2 is output in the second field. Both the video signal thus obtained by switching and the synchronizing signals supplied from the synchronizing signal generator 4 are supplied to the adder 6 which combines these signals to produce a three-dimensional image video signal. Needless to say, the television camera driving pulses, field pulses, and synchronizing signals supplied from the synchronizing signal generator 4 are all in synchronizing relationship with one another.
Next, the three-dimensional display apparatus will be described. The three-dimensional image video signal produced by the three-dimensional image pickup apparatus having the above-mentioned structure is transmitted via an appropriate means to the three-dimensional display apparatus. The transmitted three-dimensional image video signal is fed into the monitor television 8 for displaying the image. Since the three-dimensional image video signal is produced by alternately selecting the video signals from the television cameras 2 and 3, the image displayed on the monitor television 8 when directly viewed appears double and unnatural, and does not give a three-dimensional effect to the human eye.
In order to view the image displayed on the monitor television 8 in three dimensions, it is necessary for the observer to view the image shot by the television camera 2 only with his right eye, and the image shot by the television camera 3 only with his left eye. That is, the image displayed on the monitor television 8 must be selected so that the image pattern of the first field enters the right eye and the image pattern of the second field enters the left eye. To achieve this object, the light signals from the monitor television 8 are selected by means of the glasses 9 having optical shutters so that the image pattern of the first field is viewed with the right eye and the image pattern of the second field with the left eye. The sync separator 7 outputs field pules synchronous with the synchronizing signals. Here it is supposed that the field pulse signals output from the sync separator 7 are at a high level for the first field and at a low level for the second field. The field pulses are supplied to the glasses 9 to alternately operate the optical shutters provided therein, thus selecting the light signals from the monitor television 8 between the right and left eyes. To describe specifically, during the first field, the optical shutter for the right eye of the glasses 9 transmits the light while the optical shutter for the left eye blocks the light. Conversely, during the second field, the optical shutter for the left eye of the glasses 9 transmits the light while the optical shutter for the right eye blocks the light. The light signals from the monitor television 8 are thus selected, making it possible to view the image in three dimensions.
The outline of the optical shutters will be described. A mechanical shutter may be used as the optical shutter, but here we will describe an optical shutter using a liquid crystal. A liquid crystal shutter is capable of transmitting and blocking light by controlling the voltage applied to the liquid crystal, and has a sufficiently fast response to the field scanning frequency of the television camera. It also has other advantages of longer life, easier handling, etc., as compared with the mechanical shutter.
Referring to FIG. 6, the liquid crystal shutter will be briefly described. FIG. 6 is a schematic diagram of an object image. The numerals 10 and 11 indicate deflector plates, the numeral 12 a liquid crystal, the numerals 13 and 14 transparent electrodes, the numeral 15 is a rectangular wave generator, the numerals 16 and 17 are AND circuits, the numerals 20 and 21 capacitors, the numeral 18 an inverter, and the numeral 19 a field pulse input terminal. The optical shutter is basically constructed so that the liquid crystal (twisted nematic type) 12 is interposed between the two kinds of deflector plates 10 and 11, and that an electric field is applied to the liquid crystal which transmits or blocks light to serve as an optical shutter. Since the twisted nematic type liquid crystal is well known in the art, its description is omitted.
The deflector plates, the liquid crystal, and the transparent electrodes constitute the optical section of each of optical shutters 100 and 200. The deflector plate 10 transmits only the horizontal polarization wave of the light transmitted from the object, while the deflector plate 11 works to transmit only the vertical polarization wave. The transparent electrode 14 is grounded. The transparent electrode 13 is used to apply an electric field to the liquid crystal 12. In the above construction, when a voltage is not applied to the transparent electrode 13, the horizontal polarization wave transmitted through the deflector plate 10 is phase-shifted to a vertical polarization wave when it passes through the layer of the liquid crystal 12, and the vertical polarization wave passed through the layer of the liquid crystal 12 is transmitted through the deflector plate 11. This means that the liquid crystal shutter is in a permeable state, allowing the light from the monitor television to reach the human eye. On the other hand, when a voltage is applied to the transparent electrode 13, the horizontal polarization wave transmitted through the deflector plate 10 is not phase-shifted, but passes through the layer of the liquid crystal 12, retaining the state of the horizontal polarization. Therefore, the horizontal polarization wave passed through the layer of the liquid crystal 12 cannot permeate the deflector plate 11. This means that the liquid crystal shutter is in a non-permeable state, preventing the light from the monitor television from reaching the human eye. The transparent electrode 14 is grounded, as previously noted, and a driving signal is supplied to the transparent electrode 13 via the capacitors 20 and 21. The driving voltage applied to the transparent electrode 13 is approximately 10 V, and the driving frequency is approximately 200 Hz. The driving signal is produced using the rectangular wave generator 15, the AND circuits 16 and 17, the inverter 18, and the field pulse input terminal 19. To describe in detail, the rectangular wave generator 15 is caused to generate a rectangular wave of approximately 200 Hz, and the output signal from the rectangular wave generator 15 is supplied to the AND circuits 16 and 17 simultaneously. To the AND circuit 16, the field pulse which is at a high level for the first field and at a low level for the second field is supplied via the field pulse input terminal 19. Therefore, the driving signal for the liquid crystal layer is derived from the AND circuit 16 only when the first field is being reproduced. On the other hand, the field pulse supplied via the field pulse input terminal 19 is inverted by the inverter 18, and then supplied the AND circuit 17. Thus, the driving signal for the liquid crystal layer is derived from the AND circuit 17 only when the second field is being reproduced. The crystal shutter is constructed in this way. Namely, the light is allowed to pass through the right side shutter 100 of the glasses 9 shown in FIG. 6 during the reproduction of the first field, and through the left side shutter 200 of the glasses 9 during the reproduction of the second field.
However, the three-dimensional image pickup apparatus having the above-described structure requires two television cameras, thus making it expensive to construct the system. Also, since two television cameras are used to shoot the same object, preciseness is required in adjusting the shooting angles, the focusing, the angle between the two television cameras to the object, and other settings. Therefore, the above construction requires a lot of time for adjustment as compared with the time needed for shooting the object, and thus lacks mobility.